The present invention relates to a circuit of encoding a composite image signal by synthesizing the composite image signal especially for use in a television, and more particularly to a circuit and method for encoding a color television signal, which improves a resolution of the display image and removes interferences between a chrominance signal and a luminance signal by pre-filtering, in use of a pattern and motion adaptive variable bandwidth filter.
Recently, a digital signal processing technique is employed more frequently as a method to improve the quality of an image signal. Especially, in an IDTV (Improved Definition TV) and EDTV (Enhanced Definition TV), a motion adaptive signal processing technique is used for a digital filter that separates a chrominance signal and a luminance signal; and a scanning line conversion circuit that converts an interlaced scanning image signal with 525 scanning lines into a non-interlaced scanning image signal. By using the method stated above for a television receiver, it is possible to improve the resolution of the display image by efficiently removing cross luminance, components which occur a chrominance signal is mixed to a luminance signal, and cross color components which occur when a luminance signal is mixed to a chrominance signal.
A prior art for achieving the improvements as stated above is shown in FIG. 1 wherein a luminance signal Y and the color difference signals R-Y (I) and B-Y (Q) are separated respectively from the red (R), green (G), and blue (B) color signals which are applied to a gamma correction matrix 4. The color difference signals I, Q are filtered by the corresponding low pass filters 10, 11 and modulated by a quadrature phase modulator 5 according to a chrominance sub-carrier signal 1 and a burst flag signal 2.
The signal output from the quadrature phase modulator 5 and the luminance signal Y from the gamma correction matrix 4 are combined at a mixer 6 according to an input signal 3 which is a synchronous and blocking pedestal signals. To obtain a resulting encoded video signal CV, the combined signal output from the mixer 6 is low-pass-filtered by the low pass filter 8.
Since the stated prior art is not a fundamental processing method which removes the cross luminance components from the luminance signal and the chrominance signal, low quality in a resolution of the display image and interference of the image by the chrominance signal and the luminance signal often follow.